There have been many control and power designs for center pivot irrigation systems and some provide features and advantages which are very important depending upon the particular location and application. Some examples of typical center pivot systems include U.S. Pat. Nos. 3,672,572; 3,797,517; 3,802,627; 3,902,668; and 3,979,062, the disclosures of which are hereby incorporated by reference. Some considerations in designing the controls and drive include the amount of available water and its pressure, the availability of electric power, the complexity of the system both from an initial cost and ease of maintenance standpoint, and safety is always an important consideration.
The spinner drive system is one type of drive system which has been developed but the prior art designs generally have drawbacks which limit their effectiveness. A spinner drive system is generally characterized by a rotating arm driven by the pressure of the water in the main conduit which rotates a drive shaft to turn the wheels of a support tower and thereby drive the conduit through the field. This basic design benefits from its simplicity, but there are several requirements of a center pivot system which must be met by some additional complexity. One such requirement is that some method must be devised to control the relative speeds of the drives for the support towers. Support towers near the pivot or center of the revolving conduit move much slower than support towers near the outer end. In the prior art, this problem was solved by throttling the supply of water to the spinner. A reduced water pressure and flow through the spinner arm results in a slower revolution of the arm and a slower drive speed. However, by reducing the pressure and flow of water to a spinner, the driving torque is correspondingly reduced which significantly reduces the ability of an inner, slower moving support tower to traverse ridges and valleys in the field. This is a significant drawback and greatly limits the terrain that the spinner drive system can be used on.
Other prior art designs have solved the torque and speed problems by providing a control system to cycle the spinner drive off and on so as to achieve an average speed, much as in the electric drive systems. Although the average speed system solves the torque problem, many of the prior art designs use complicated mechanical linkages and/or electrical controls with electrical lines extending along the length of the conduit and in close proximity to the large quantities of water delivered through such an irrigation system. As can be appreciated, an electrical control system increases the initial cost of the system, extends the maintenance and troubleshooting problems from simple hydraulics to include electrical circuits, and requires a source of electricity (or increased capacity if an electrical pump is required) for achieving proper irrigation.
An average speed drive solves the torque problem but creates another as it is impossible, without more, to vary the amount of water applied to the field with an average speed spinner drive system. This is because once a drive gear ratio is chosen, each support tower sweeps through a given area of field for a given number of revolutions of the spinner. A given number of revolutions of the spinner applies a given amount of water to the field, assuming no change in water pressure. Therefore, a given amount of water is applied to the field because changing the speed of the system by changing the ratio of on/off time does not change the total number of revolutions required for each support tower to traverse the entire field. As can be appreciated, this greatly limits the versatility of what may be a rather expensive irrigation system as each system would be limited to delivering only one amount of water without complicated and time consuming mechanical changeover of the gearboxes or spinner nozzles.
Applicant has solved these problems of the prior art by developing an average speed spinner drive system which utilizes totally hydraulic and mechanical controls while providing a variable water application rate. Applicant's system may also be easily converted for reverse rotation in the field which is highly desirable in those applications that make it impossible for the irrigation system to rotate continuously through the field because of buildings or other obstructions. As there are no electrical controls in applicant's system, there are no expensive and potentially hazardous runs of electrical lines along the length of the conduit which minimizes the maintenance costs and complexity. This also enhances the versatility of the system by enabling it to be used in remote locations where there is no available electrical power except that produced by a small generator used to pump the water. Applicant's system is an elegantly unique combination of valve controls for each support tower which use a mechanical linkage to detect a misalignment with an adjacent section of conduit, and sequence on the spinner drive at its associated support tower to move the section of conduit back into alignment. The outermost tower is the master tower which leads the system through the field. It is controlled by a selectively adjustable percentage timer which has adjustable cams for sequencing on and off its spinner drive. An overwatering timer on one of the inner tower assemblies detects when a spinner drive has not been sequenced on for a preselected period of time such that some malfunction in the speed control is highly likely. The overwatering timer then shuts down the entire system.
As mentioned, applicant's system combines the advantages of an average speed spinner drive system with a wide range of adjustability in the amount of water applied to the field, with the amount applied being directly proportional to the speed of the system through the field. Applicant accomplishes this with a first group of sprinklers along the main conduit which are continuously on and a second group of pairs of sprinklers which are sequenced on only when an associated spinner drive is sequenced off. Each of the pairs delivers substantially the same amount of water as its associated drive and to substantially the same area of field. Also, the first group of sprinklers delivers substantially the same amount of water per unit of field area as do either the spinner drive or its associated sprinkler pair. Thus, there is no difference between the amount of water received by the section of field being irrigated with the spinner-sprinkler combination as that being irrigated by the continuously on sprinklers. In this manner, the amount of water applied is directly proportional to the speed of the system and a substantially even coverage of the field is achieved.
Applicant's spinner drive system and control has other features and benefits which are more fully explained, along with the preceding features, in the description of the preferred embodiment and drawings which follow.